TrigeminalNerveInjuryandManagement
KristopherLeeBScDDS,MD,FRCD(c),DipABOMS
StaffSurgeon,OralandMaxillofacialSurgeryMountSinaiHospital
Outline
• Reviewofanatomy• Mechanismsofinjury• InjuryclassificaLon• Diagnosis,neurosensorytesLng• Management• Outcome
Anatomy
• 669LNsfrom430cadavers• 14%LNabovelingualcrest• AtitstypicallocaLon,
meandistanceisV=3mm,H=2mm
• 22%LNindirectcontactwithlingualplate
Microanatomy
• 4connecLveLssuesheaths– Mesoneurium– Epineurium– Perineurium– Endoneurium
• Vasonervorum• LymphaLc• Nervefiber
NeuralFascicularPaZerns
IANandlingualnervesarepolyfascicularmoreresistanttoneedleinjuryalmostimpossibletoalignfascicle
FibertypesA-alpha- Largestmyelinatedfibers- 6-8umdiameter- ConducLonvelociLesof70-120m/s- Associatedwithmusclespindles,tendonafferents,andskeletalmuscleefferentfibers
A-beta- Myelinatedneuron- 6-8nmdiameter- ConducLonvelociLesof30-70m/s- Sensibilityoftouch
FiberTypesA-delta- Smallestmyelinatedneurons- 2.5-4um- ConducLonvelociLesof12-30m/s- SenseoftemperatureandfastpainC-fibers-unmyelinated- 1umdiameter- Transmitat0.5-2m/s- TransmitsLmuliencodedforsloworsecondpain,temperature,andefferentsympatheLcfibers
Terminology
• Anesthesia–absenceofanyresponse• Paresthesia–abnormalsensaLon,spontaneousorevoked,notunpleasant
• Dysesthesia–unpleasant,abnormalsensaLon• Hyperaesthesia–increasedsensiLvitytoeitherofpainfulornonpainfulsLmulaLon– Allodynia-painfromanordinarilynon-painfulsLmulus
– hyperalgesia
• Neuralgia–paininthedistribuLonofanerveornerves
• Neuropathy–adisturbanceoffuncLonorpathologicchangeoffuncLonofanerve,excludingdescripLonofinjury
Mechanismofinjury- Compression- Stretch- LaceraLon- Compartmentsyndrome- Chemicalinjury
MechanismofInjury- TraumaLc
- Jawfracture
- Iatrogenic- Localanesthesia- OralSurgery:ExtracLons,Implants,bonegraeing,orthognathicsurgery,ablaLvesurgery
- Periodontalsurgery- EndodonLcs- Chemical:endodonLcmaterials,hemostaLcagents
3rdMolarextracLon
• Rangesfrom0.4%to22%,mosttypicallyreportedas5%
• Spontaneousrecoverywilloccurinasmanyas75%ofthesein6monthsto1year
• Resultsina0.5%to2%permanentparesthesiarateforIANandLN
RiskFactorsforIAN/LNinjurywith3rdmolars
• Age>35• DepthofimpacLon• Generalanesthesia?• AngulaLon• Lingualordistoangular• Integrityofthelingualcortex• NeedfortoothsecLoning• Surgeonexperience• OperaLveLme• IntraoperaLveexposureofthenerve• Rood’spanoramicindicators
Rood’sfeaturesofmandibular3rdmolarandIANanatomy
• LossofcorLcaLonofthecanal• ConstricLonofthecanal• DeflecLonofcanal• Shadowingofroots• Narrowingofroot• Darkening/bifidrootapex
• Incidenceofnerveinjurycanbe20-36%
NerveinjurywithlocalanesthesiainjecLon
• PogrelesLmatedincidenceat1:26,000to1:160,000
Overallincidence:1inmanymillionsPrilocaine4%:1in2millionsArLcaine4%:1in4millions
• PotenLalmechanisms:-ChemicalinjurypossiblyrelatedtoanestheLcconcentraLon(4%)- Directneuraltrauma,laceraLonfromabarbedneedle- Intraneuralhematoma
InjecLoninjuries• Difficulttopredictorprevent• ElectricshocksensaLonuncommoninthosewhosustain
injury• Non-anatomicdistribuLonofsymptomspossible• Morecommoninfemales• Lingualnervemorecommonlyaffected(greaterstretch
withmouthopening??)• Majorityofcasesresolvein8weeks• IflasLngmorethen8weeksthenonly1/3resolve
spontaneously• Dysesthesiamorecommonwiththistypeofinjury• SurgeryisapooropLon
InjuryfromendodonLctreatment
• OverinstrumentaLon• ExtrusionofendodonLcmaterial• ManagementinvolvespromptsurgicalexploraLon,washout,externalneurolysisornervegraeasneeded
InjuryfromdentalImplants
• Mostcommonwithposteriormandibularimplants
• Injuryhappensmostlikelyfromtwistdrillsratherthandirectcompressionoffixure
• Hematomacausingcompartmentsyndrome• Managementinvolvesremovalofimplantoncerecognizedinthepostopperiod
• Dysesthesiaareverycommonwiththeseinjuries
Strategiestoavoidinjury
• PreoperaLveCBCT• Drillstops• Shortimplants
HemostaLcagents
• SurgicelhasimmediatedamagingeffectsonnervefuncLon
• Itappearsthatbonewax,bovinecollagenfibrils(Avitene),gelfoamarebenigntonervefuncLon
ClassificaLonofNerveInjuries
• SeddonClassificaLon• Sunderland• DellonandMackinnonmodificaLonofSunderland
Seddon
• Neuropraxia• Axonotmesis• Neurotmesis
Neuropraxia
• AconducLonblockduetoanoxiafrominterrupLonofepineurialorendoneurialbloodsupply–includesinterfascicularedema
• NoaxonaldegradaLonordemyelinaLon• Completerecoverywithin24hrsto2months• Aphysiologicnotanatomicinjury• Ifischemiaisprolonged,ahighergradeinjurywillresultfrominfarcLonandsubsequentfibrosis
• (Sunderlandfirstdegreeinjury)
Axonotmesis
• AxonalinjurywithsubsequentdegeneraLonandregeneraLon
• OccurswithoutdisrupLonofendo/peri/epineurium
• IniLalanesthesiawithTinel’ssign• Completerecoverywithin12months,onsetofsensoryreturnwithin2-4months
(Sunderland2nddegreeinjury)
Neurotmesis
• SeveredisrupLonoftheconnecLveLssuecomponentsofthenervetruckwithcompromisedsensoryandfuncLonalrecovery
• Sunderland3rd,4th,5thdegreeinjurydependingonwhichofthethreelayersaredisrupted
• Immediateanesthesiawithpossibledevelopmentofparesthesiaorneuropathia
Sunderland
SunderlandGrade6injury
• DescribedbyDellonandMcKinnonin1988• RecognizestheheterogeneityofpresentaLonanddiagnosLcambiguitytypicalofperipheralnerveinjurieswhereinfeaturesofallclassesmaybepresent
Consequencesofinjury• Complexstructural,metabolicandphysiologicchanges
• Changesoccurthelengthofnerve,notjustatsiteofinjury
• “injurycurrent”generatedwithinfluxofNa+,andCa++ionstriggeringpleiotropicenzymaLcandtranscripLonalacLvity.
IneffecLveHealing-neuromas
• Disorganizedmassofcollagenfibersandrandomlyorientedsmallnervefascicles
• Classifiedaccordingtotheirgrossmorphology
Management
PaLentEvaluaLon
• History• SubjecLvesensaLon,0-100%• ObjecLveneurosensorytesLng• Clinicalexam
ClinicalExam
• Ideally1sttestconductedwithin2weeksfollowinginjurytoestablishpostopbaseline– Thenfollowonceamonth
ClinicalExam• Neurosensorytest– Mappingofinvolveddermatome– StaLclighttouch– BrushdirecLonaldiscriminaLon– TwopointdiscriminaLon– Pinprick/nocicepLon– ThermaldiscriminaLon
• Determinepresenceofsensorydeficit,typeandmagnitudeofdeficit
• DocumentobjecLvelythelevelofsensaLonforfuturecomparison
Mappingoftheinvolvedarea
SLmuluslocalizaLon
• EsLmatetheamountofsynesthesia• WithwoodenendofcoZonswab• Shouldlocalizewithin1-2mmofsLmulus
TwopointdiscriminaLon
• AssessthedensityandquanLtyoffuncLonalsensoryreceptorsandafferentfibers
• A-delta,C-fibers• Boleygauge/Caliperat1mmincrements
TwopointdiscriminaLon
BrushdirecLonaldiscriminaLon
• A-alpha,A-beta,lanceolateendings,PaccinianandMessinercorpuscles
• PropriocepLon• SeriesofrandomdirecLons,usingcoZonswap
StaLclighttouch• Merkelcell,Ruffiniending,andA-betaintegrityrequired
• Weinstein-semmesfilament/vonfreyfilaments
NocicepLon
• Assessfreenerveendings–CandA-deltafibers
• Use27gaugeneedle• PresswithoutindentaLonàpaLentabletofeel=normalresponse
• PresswithindentaLonàabnormalresponse
ThermaldiscriminaLon
• AdjuncLve,andnotveryuseful• Integrityofsmalldiametermyelinatedandunmyelinatedfibers
• WarmthaZributedtoA-deltafibersandcoldtoC-fibers
DiagnosLcnerveblocks
• Aidtolocalizesiteofinjury• Usefulinneuropathicpain• Helpsdeterminewhetherpainiscentrallyorperipherallymediatedorwhatdegreeofeach
ClinicalExam
• EvaluaLonofwound• PalpaLonforTinel’ssign(lingualnerve)• PalpaLonforneuroma(lingualnerve)• Panorex:ruleoutforeignbodies/rootLpscompressingnerve
Medicalmanagement
• Mostlylimitedtodysesthesia/neuropathicpain
Surgicalmanagement
• Dilemma:allowingenoughLmeforspontaneousrecoverybutnotsomuchtoimpairsurgicaloutcome
• WhyisLmethoughttobecriLcal?– DistalnervedegeneraLon– Ganglioncelldeath– CentralcorLcalchanges
SurgicalManagement
• Decidewhetherornottorepairorobserve• Takeintoaccountthetype,mechanism,severity,andlocaLonofnerveinjury,paLent’sdesireswithrespecttotreatment.
SurgicalmanagementIndicaLons:• Evidenceofnervecompression–immediateremovalof
theobject(rootLp,bonefragment,implant)• EndodonLcmaterial–mayrequireimmediatewashout,
decompression• WitnessedtransecLon–mayrequireimmediaterepair• Closedinjury:followmonthly.Repairifnoimprovement
at1-3monthsforLN,3-6monthsforIAN• Orpainat4months
Outcomes
Outcome
Postopcourse
• Variableperiodofcompleteanesthesia,typically3month
• Regrowthoccursat1mm/dtherefore3cmpermonth
• Occursmoreslowlywithnervegrae• Dysesthesiaisalwayspossibleaeeranynervesurgery
Keypoints• SpontaneousrecoveryhappensinsomebutnotallpaLents.Difficulttopredictwhowillfallintowhichcategory(letusmakethatdecision)– witnessedtransecLonmayrequireimmediaterepair– OtherwisewefollowwithrepeatneurosensorytesLng,andrepairwhenindicated:• forLNat1-3months,IANat3-6months,ifparesthesiaissignificantandnoimprovement
• Painat4months• Ifparesthesiaisimproving,conLnuetofollow
• IANrecoversmoreoeenthanlingualnervebecauseofbonyconduit
Keypoints• InjecLoninjuriesarepoorsurgicalcandidates– Mostresolvesaeer8weeks,ifnot,only1/3willimprove
• Dysesthesiaisverydifficulttomanage.Responsetosurgeryishighlyunpredictable.MostpaLentsneedlongtermmanagementwithmedicaLons
ThankYou